This invention relates to a focal point coincidence sensing device and more particularly to a device for sensing a coincidence of focal point so as to record an image of the object to be photographed.
In this field of art, various kinds of sensing devices have been proposed. One of them was made such that two light paths, a fixed light path and a movable light path which could change information representative of the distribution of a light intensity, were arranged such that the incident lights coming from the two light paths were received from or by two light-receiving devices composed of a plurality of light-receiving elements, a ratio between the outputs of the light-receiving elements corresponding to the two light-receiving devices was calculated, and a point nearest to the value of 1 in the ratio was sensed and thereby the focal point coincidence signal was generated. However, since the value nearest to the ratio of 1 was sensed, it was necessary to scan the overall operational range of the movable incoming or incident lights and the sensed values were apt to be affected by a difference in the light paths.
In order to eliminate these disadvantages, the applicant has provided a sensing device in the Japanese Patent Application Ser. No. 138740/1977 in which a light-receiving device having a plurality of light-receiving elements is utilized, in the first step, a ratio between the outputs of each of the elements corresponding to a distribution of a light intensity of the incident light coming from the fixed light path is calculated and stored in a memory circuit, and in the second step, a ratio between each of the elements corresponding to a distribution of the light intensity of the incident light coming from the movable light path or the incident light coming from the fixed light path and the movable light path is calculated and the focal point coincident signal is generated when the result thereof coincides with the ratio stored in the first step.
However, such a sensing device has the disadvantage that the ratio stored in the first step and the ratio calculated in the second step often do not coincide with each other due to the fact that the distribution of the light intensity of the incident light entering into the fixed light path and the distribution of the light intensity of the incident light entering into the movable light path do not always coincide with each other.